A trimmable RC-oscillator for automotive applications, with low process, supply, and temperature sensitivity

The design of a stable over temperature RC-oscillator for automotive applications is presented in this paper. The oscillator is designed and fabricated in a 0.35 mum BCD6 technology, using a 3.3 V supply voltage. The stability over temperature of the oscillation frequency is quite independent on process and supply voltage variations: the oscillator shows a frequency drift from 27degC lower than 0.5% in all conditions (supposing to use an off-chip ideal resistance), over a temperature range from -40 to +125degC and a plusmn10% supply voltage variation around its typical value. A topology exploiting two capacitors driven by non-overlapping phases is proposed to ensure the proper timing for charge and discharge. A digital trimming is also provided to compensate process variations. The nominal output frequency can be set up to about 1 MHz simply by changing the value of the external resistor. Detailed circuit design and simulation results are presented.